Fortunately, when I moved and got the new Fios router that does N, I suddenly realized that every WiFi device I have is N, so I just set it to N-only. You might want to look closely at the devices you think don't do N. I thought some of my stuff was too old for it, but was surprised when I did a little research and found that it wasn't.

*edit*

Plus, I'm not too worried about guests. We just had family visit, and between them they had two iPads (gen 3 or newer), two iPhones, and an Air. Most of our guests come over with smartphones, and the majority of those are capable of 802.11N it seems...